A spindle assembly used to rotate and hold a machine tool or workpiece typically comprises inner and outer coaxial shafts having front and rear ends and extending along a common axis with the inner shaft axially displaceable in the outer shaft, a holding device or chuck on the front ends adapted to grip a tool or workpiece in an axially outwardly displaced position of the inner shaft relative to the outer shaft, a coupling ring fixed on the rear end of the outer shaft, and an actuator having a piston axially engageable with the rear end of the inner shaft and operable to axially shift the inner shaft in the outer shaft. Springs normally urge the inner shaft inward so, absent pressurization of the cylinder surrounding the piston, these springs maintain the assembly in the holding position in which it solidly grips the workpiece or tool. When thus held, the shafts are rotated at high speed for the desired machining operation.
The spindle assembly described in US Pat. No. 5,865,578 has inner and outer coaxial shafts having front and rear ends and extending along a common axis with the inner shaft axially displaceable in the outer shaft, a holding assembly on the front ends adapted to grip a tool or workpiece in an axially outwardly displaced position of the inner shaft relative to the outer shaft, a coupling ring fixed on the rear end of the outer shaft, and an actuator having a piston axially engageable with the rear end of the inner shaft and operable to axially shift the inner shaft in the outer shaft. Complementarily interengaging formations on the actuator and the coupling ring including a is groove and a projection are displaceable between a holding position axially securing the ring on the actuator and a freeing position allowing the ring to be axially separated from the actuator.
When the actuator is connected with the shafts, the formations can be engaged together to allow the actuator to operate the chuck. In this position the holding device can be opened to allow a workpiece or tool to be taken off or set in place, to which end the actuator axially displaces the piston into an outer end position. Once the tool or workpiece is properly engaged in the holding device, the shafts can be rotated to perform the desired machining operation.
In order to prevent the actuator from rotating with the shafts and to surely separate the rotating parts--the shafts and holding device--from the nonrotating parts--the actuator--the two relatively movable parts of the housing are pushed apart by compression springs so that the formations can move out of contact with one another. To dechuck the tool or workpiece the piston is moved oppositely so that the formations are again engaged and as a result the shaft bearings are relieved of forces from the piston. This relief is not complete since the bearings must at least take up the force of the springs used to relatively displace the housing parts.